“It’s important that residents in these communities take immediate steps to protect themselves and their families from mosquito bites,” public health veterinarian Catherine Brown said in a press release.

“People need to continue to use insect repellent, cover up exposed skin, and avoid being outdoors at dusk and after nightfall when mosquitoes are at their most active.”

Get Fast Forward in your inbox:

Forget yesterday's news. Get what you need today in this early-morning email.

The state also has raised the risk level to moderate in Abington, Braintree, Brockton, East Bridgewater, Hingham, Holbrook, Norwell, and Pembroke because of their proximity to the area of highest risk.

The Norfolk County victim, a woman in her 80s who was hospitalized this month, was the state’s first confirmed Eastern equine case and death this year. Last year, seven people were infected, and three of them died.

In the western half of the state, the Eastern equine risk level was already listed as critical in Belchertown and as high in adjacent Amherst.

The state said the disease begins with a high fever, often 103 to 106 degrees Fahrenheit, stiff neck, headache, and lethargy, symptoms that appear three to 10 days after a bite from an infected mosquito.

The disease can progress quickly to encephalitis, an often lethal inflammation and swelling of the brain.

To avoid mosquito bites, which can also transmit West Nile virus, residents are urged to use insect repellent; stay indoors between dusk and dawn, when the insects are most active; and wear long-sleeve shirts, long pants, and socks when outside.

State officials also ask residents to drain standing water, where mosquitoes lay their eggs.